Levodopa-Induced Dyskinesia Is Associated with Increased Thyrotropin Releasing Hormone in the Dorsal Striatum of Hemi-Parkinsonian Rats

Background Dyskinesias associated with involuntary movements and painful muscle contractions are a common and severe complication of standard levodopa (L-DOPA, L-3,4-dihydroxyphenylalanine) therapy for Parkinson's disease. Pathologic neuroplasticity leading to hyper-responsive dopamine receptor signaling in the sensorimotor striatum is thought to underlie this currently untreatable condition. Methodology/Principal Findings Quantitative real-time polymerase chain reaction (PCR) was employed to evaluate the molecular changes associated with L-DOPA-induced dyskinesias in Parkinson's disease. With this technique, we determined that thyrotropin releasing hormone (TRH) was greatly increased in the dopamine-depleted striatum of hemi-parkinsonian rats that developed abnormal movements in response to L-DOPA therapy, relative to the levels measured in the contralateral non-dopamine-depleted striatum, and in the striatum of non-dyskinetic control rats. ProTRH immunostaining suggested that TRH peptide levels were almost absent in the dopamine-depleted striatum of control rats that did not develop dyskinesias, but in the dyskinetic rats, proTRH immunostaining was dramatically up-regulated in the striatum, particularly in the sensorimotor striatum. This up-regulation of TRH peptide affected striatal medium spiny neurons of both the direct and indirect pathways, as well as neurons in striosomes. Conclusions/Significance TRH is not known to be a key striatal neuromodulator, but intrastriatal injection of TRH in experimental animals can induce abnormal movements, apparently through increasing dopamine release. Our finding of a dramatic and selective up-regulation of TRH expression in the sensorimotor striatum of dyskinetic rat models suggests a TRH-mediated regulatory mechanism that may underlie the pathologic neuroplasticity driving dopamine hyper-responsivity in Parkinson's disease.Morris K. Udall Center for Excellence in Parkinson’s Research at MGH/MITNational Institutes of Health (U.S.) (NIH NS38372)American Parkinson Disease Association, Inc.University of Alabama at BirminghamMassachusetts General HospitalNational Institute of Diabetes and Digestive and Kidney Diseases (U.S.) (NIDDK/NIH grant R01 DK58148)National Institute of Neurological Disorders and Stroke (U.S.) (R01 NINDS/NIH grant NS045231)Stanley H. and Sheila G. Sydney FundMichael J. Fox Foundation for Parkinson's Researc

Dysregulation of Caldag-Gefi and Caldag-Gefii Predicts the Severity of Motor Side-Effects Induced By Anti-Parkinsonian Therapy

Voluntary movement difficulties in Parkinson's disease are initially relieved by L-DOPA therapy, but with disease progression, the repeated L-DOPA treatments can produce debilitating motor abnormalities known as L-DOPA-induced dyskinesias. We show here that 2 striatum-enriched regulators of the Ras/Rap/ERK MAP kinase signal transduction cascade, matrix-enriched CalDAG-GEFI and striosome-enriched CalDAG-GEFII (also known as RasGRP), are strongly and inversely dysregulated in proportion to the severity of abnormal movements induced by L-DOPA in a rat model of parkinsonism. In the dopamine-depleted striatum, the L-DOPA treatments produce down-regulation of CalDAG-GEFI and upregulation of CalDAG-GEFII mRNAs and proteins, and quantification of the mRNA levels shows that these changes are closely correlated with the severity of the dyskinesias. As these CalDAG-GEFs control ERK cascades, which are implicated in L-DOPA-induced dyskinesias, and have differential compartmental expression patterns in the striatum, we suggest that they may be key molecules involved in the expression of the dyskinesias. They thus represent promising new therapeutic targets for limiting the motor complications induced by L-DOPA therapy.WoSScopu